The Revised - Latin Primer

The 1906 edition is available for free through Archive.org .

It popularized a new structure for learning noun endings, starting with the nominative, vocative, and accusative, which helped highlight similarities between these cases. The revised Latin primer

It is still in print and available from publishers such as Longman. If you're studying with this book, Find a seller for a physical copy? The 1906 edition is available for free through Archive